Instantaneous tachometer method and apparatus



Dec. 27, 1949 R. K. BoLgAND ETAL 2,492,617

INSTANTANEOUS TAGHOMETER METHOD AND APPARATUS Filed llarch 19. 1945 2`Sheets-Sheet 1 busi, kwlnk jlul Dec. 2,7, 1949 R. K. BOLAND Erm. 2,492,617

I-NsTANTANEoUs TACHOMETER METHOD AND APPARATUS Filed March 19, 1945 2 Sheets-Sheet 2 MTE FOREXMPLE= 40-240 PER MIN. K 6 E C I TERM/NHLS 30M() 5'/ II I I I F/G. 5 I-Ai I P01. AGE OFPLTE TIME "/10ETERMINEO BY MI'DNENTS l I TEEM/ML 5g 0l' Vl /N T/E MllLT/V/BRATOR CIRCUIT I I /G.4 I vvv/se oFPLA-re l I TERQIML 4a of v2 I I I l I l I 87-/0l0f' TRANSFER B waas Mya@ TIMES 'BR CDETERM/NED BY R/2 l' C5 @ma coNoocT/vf awr/NG T/ME "a" NEGT/VE Fl/LSE BVR/)V6 TIME 'C "IMS N0 E/IIFECT I I F/C I ID 501.7365 0F GRID 8l oF T055. W

la EMDWT/VE DUR/NG TIME "E'i NEGATIVE Pl/L 5E HIRING TIME "D" HAS lA/0 EFFECT =/G.7 l I I vo/.n Ackoss calvo.

c5. fusa, s/M/LARLY F Ar Pura oF Ve z car/loos aF Vs THRU /STCAT/lEFLLowER vannes Ar /s Passso THRU rRANsFER ruses I6- x Le To Cfu/PGE C8 /7' ls PIRONET/@NAL To T/ME "K"M/Nus THE CONSTANT A V VEN TORS ,6u PH A. o/ A ND o YA/To/v G. MGA/MAN Q7 WMA/@WM Patented Dec. 27, 1949 INSTANTANEOUS TACHOMETER METHOD AND APPARATUS Ralph x. Bouma and Boynton o. maman. Rochester, Minn., assignors to Waters Conley Company, Rochester, Minn., a corporation of Minnesota Application Maron 19, 1915, sonal No. saam This invention relates to a method and apparatus for establishing an operating condition in an indicator or work circuit. which is the i'unction of the time interval elapsing between successive signal impulses that are received, and particularly to a cardiotachometer of the instantaneous reading type. Instruments heretofore available for the indication or recording of heartbeat impulses have been of several general types. In one type of electro-cardiographic apparatus the input signals generated by the heartbeat of the patient have been amplified and merely recorded on an oscillograph of the usual photographic recording type or of the cathode ray type. Where utilizing a cathode ray oscillograph there has been provided a wave form indication corresponding to that of the heartbeat impulse. By utilizing the ordinary photographic recording oscillograph, a permanent record is made of the heartbeat:l impulse wave form and by scaling and amplitude measurements of the photographic record, it has been possible to determine the rate, strength and other factors of importance in the heartbeat signal.

The photographic type of cardiographic instrument is disadvantageous from the standpoint of the amount of mechanism required for its use and also disadvantageous because it has been necessary first to develop and then scale the photographic record of the input signal to determine the indications. This is a cumbersome and timeconsuming operation and as a consequence this method has not been readily adaptable for portable installations nor has it provided the attending physician with a readily available visible indication of the instantaneous heartbeat rate as is desirable in diagnostic work. Other heartbeat rate indicators have not provided any indication of the instantaneous rate but only an average value with the result that the attending diagnostician has not been provided with any indicatio of irregularities that may occur.

It is therefore an object of the present invention to provide a method and apparatus capable of furnishing instantaneous indication of the time elapsing between successive impulses received and specifically to provide a cardiographic tachometer of the instantaneous type. It is also an object of the invention to provide an apparatus capable of furnishing at its output a voltage or other electrical characteristic, the magnitude of which corresponds `or bears a deiinite relationship to the time elapsing between successive impulses received.

Other and further objects of theinvention are 17 claims. (or 12s-aos) those inherent in the apparatus herein illus-l trated, described and claimed.

The invention is illustrated with reference to the drawings in which Figure 1 is a wiring diagram of the apparatus of the present invention; and' Figures 2-7 are a series of correlated graphs indicating the performance of the method and apparatus vof the present invention.

Referring to Figures 1-7, the method and apparatus of the present invention have been developed for the speciiic purpose of instantaneously indicating the time intervals elapsing between successive heartbeats (instantaneous pulse rate) and will be explained hereinafter with reference to this specific type of apparatus, but it is obvious that there are many other applications in lili which the invention may be utilized. In cardiotachometer usage the frequency rate of pulse varies from about 40 to 240 beats per minute. but by appropriate selection oi' constants, the invention may be caused to function throughout other ranges of rates, and by utilizing other indicating or responsive apparatus the invention may, therefore, be applied to widely varying frequency rates.

Websters New International Dictionary, 2nd edition, 1939, G. 8i C. Merriam Co. deiines, An electrocardiograph is an instrument for recording the changes of electrical potential occurring during heartbeat, as by photographing vibrations of a string galvanometer connected to the right and left hands, or with one hand and one foot. In accordance with the present invention, for cardiotachometer usage a voltage signal is picked up by means of electrodes applied to the patients body and the signals so provided are ampliiied by a resistance-coupled ampliiier of conventional type which then serves as the input to the apparatus of the present invention. The input is applied at terminals 30 and 3|, Figure 1.

In general the method of the present invention involves charging a timing capacitor through a suitable resistance and at a rate such that the voltage built up across the timing capacitor is indicative of the time elapsed since the last successive heartbeat. As each heartbeat occurs, this voltage across the timing capacitor is transferred to a holding capacitor where it is stored and utilized to provide a meter indication or to provide an output voltage, the value of which may be utilized for operation oi.' any appropriate work circuit. As soon as the voltage of the timing capacitor has been transferred to the holding capacitor (when the heartbeat signal occurs) the timing capacitor is then discharged whereupon the entire cycle is repeated. Thus, the indication given or the output voltage provided during any two heartbeats (or other received signals) is proportional to or is a function of the time elapsing between the immediately preceding heartbeat or received signal.

Referring to Figure l, under the bracket 32 there is provided a timing circuit, preferably a multivibrator capable of generating a square or abruptly rising wave of a predetermined, relatively short duration. One such timing wave is generated for each heartbeat signal received. The duration of this (preferably) square wave oi' the multivibrator is a constant in the apparatus and is chosen so that it is only a fraction oi' the time interval elapsing between heartbeats at the most rapid rate for which the system is designed. Thus, referring to Figures 2-7, the heartbeats are indicated at 33 and3'4 on Figure 2. The time interval K elapsing between successive heartbeats 33 and 34 may be any time period in the range for which the instrument is designed. For example where the instrument is used as a cardiotachometer, K may range from 1/,0 of a minute to 1/40 of a minute. The time interval A oi the negative square wave produced by the multivibrator circuit, Figure 3, i's much shorter, i'or example 1/2000 of a minute or even shorter, and is constant, regardless of variations in time K, between received signals (heartbeats).

The multivibrator timing network 32 consists of a pair of three-element tubes VI and V2 which are identical. The cathode 35 of tube Vi and cathode 36 of tube V2 are indirectly heated by their laments 35 and 36. From input terminal 3l which is grounded at 31, line 38 extends through junctions 39 and 4t and through resistors R5 and R6 to junction 42 on line 43, which is the positive voltage supply line. Input terminal is connected through line 44, condenser C1 and junction 45 to the grid 46 of tube VI, and thence through condenser C2 and line il to the plate terminal 48 of tube V2. Cathode 36 is connected by line 49 through junction 59 and thence to junction 5i on cathode line 52 of tube Vi. Capacitor C4 is connected between junction 40 on line 38 and junction 5i, and junction is connected by means of line 53 to the variable tap 54 on resistance R5. From junction 50 a connection also extends through resistor R4 to junction 56 which is the terminal of grid 51 of tube V2. From the grid terminal 56. line 58 extends through capacitor C3 and thence to the plate terminal 59 of tube VI. Junction 60 on positive supply line 43 is connected through resistor R3 Ato the plate terminal 48 of the tube V2, and line 43 is likewise connected through resistor R2 to the plate terminal 59 of tube VI. Junction 45 on the grid of tube VI is connected through resistor Ri to junction 39 on the grounded line 38, and the plate terminal 48 of tube V2 is connected through line 6| and capacitor C5 to junction 62 and thence through resistor RI2 to ground 83. l

The multivibrator circuit is theoretically capable of being stabilized at any of a variety of steady state conditions but in actual practice, due to slight electrical disturbances, the circuit is capable of vibration. In the system of this invention, the constants of the multivibrator circuit are chosen so that the multivibrator system stabilizes in the steady state with tube Vl nonconductive and tube V2 conductive'. When apositive input signal is applied to grid 46, tube Hence, the multivibrator circuit tends to oscillate,

VI becomes conductive which in turn causes the '43 ot tube V2 to become more positive. Application of this more positive voltage through condenser C2 to the grid 46 of tube VI makes the grid 4t still more positive and hence tube VI becomes even more conductive. But this cumulative action cannot continue indefinitely for one or both oi' two reasons. The current in tube Vi cannot increase indenitely because there is a. definite cut-off determined by the maximum available cathode emission from cathode 35. Likewise, tube V2 cannot decrease below a predetermined value because of the emissivity characteristics of the tube. Therefore, the voltage at terminal 48 cannot continue to increase beyond a predetermined amount and likewise the voltage at plate 59 does not decrease below a predetermined value. The transfer of voltage from plate terminal 48 to grid 46 and from plate terminal 59 to grid 51 occurs only when the voltages at the plates are changing. Hence, when the plate terminal voltages cease to change, the4 and circuits of this type are capable of producing sustained oscillations.

The reason the multivator stops after one reversal is because of the dissymmetry in bias that is introduced in the grid circuits. The potential drop across that part of resistor R5 between junctions 39 and 54 biases the grid 46 of tube Vi negatively with respect to cathode 35 so that even though the negative voltage applied through condenser C2 is diminishing, tube VI remains non-conductive until again started into an oscillation by a positive pulse on the input circuit. Then it goes through the complete oscillation as described, and again stops after one oscillation. For this reason the circuit may be designated as a "ip-iiop circuit.

The multivibrator output is illustrated in Figures 3 and 4. Figure 3 represents the voltage at the plate terminal 59 of tube VI, and Figure 4 `represents the voltage at the plate terminal 48 of the tube V2.

These output voltages are square, or nearly square, in wave form and the leading edge corresponds in time to the input pulse (time X in Figures 2-7) and the .trailing edge comes at a definite time interval later (time Y in Figures 2 7). (constant A) is determined by the values of the multivibrator circuit and once established this becomes a constant in the apparatus. Both the negative square Wave at the plate of tube VI and the positive square Wave at the plate of tube V2 are utilized for timing purposes in the invention as hereinafter more fully explained.

Referring again to Figure 1, there is illustrated a timing capacitor C6 which is connected to junctions 65 and 66, the latter being grounded through line 8G to ground terminal 68. The

timing capacitor C6 is charged through line 'lllv which extends from the grid 'Il of tube V3 through junction 65 and junction 15 and thencethrough resistor R9 to junction 16 which is 'con- The denite time interval .g nected through resistor R|0 to junction 18 on vpositive supply line 43. Line 43 extends through junction 80 and thence to the positive output terminal 8| of a direct current voltage supply,

hereinafter more fully described. The negative output terminal 82 of the voltage supply is connected through line 83 which extends through resistor R8 to the grid terminal 84 of a discharge tube V4 and thence through condenser C1 to the plate terminal 59 of the multivibrator tube VI. Terminal 16 (below resistor RIU) is likewise connected by line 86 through resistor Ril and thence through cathode terminal 81 and junction 66 to ground terminal 68. 'By utilizing low energy instruments or work circuits, the stored charge on C6 may be used directly or transferred directly as hereinafter described, but it is preferable to utilize the stored charge merely to control the output of a power source of larger capacity. For

this purpose a thermionic tube, here designated L a cathode follower, is used.

Thermionic tube V3 is a high input-impedance three-element tube and is provided with a cathode 12, grid 1I and anode 13. This tube is called the rst cathode follower, for another second cathode follower is also used as hereinafter described. Cathode 12 is indirectly heated by the filament 14. Grid 1| of tube V3 is connected to terminal 65 of the timing capacitor C6. The cathode 12 is connected through output junction 88 and thence through resistor R1 to ground terminal 68, the anode 13 being connected to junction 89 on positive supply line 43. As the voltage of the positive terminal 65 of the timing capacitor varies due to the charge accumulated upon the timing capacitor C6, the conductivity of tube V3 likewise varies and the current passed by the tube changes the voltage drop across resistor R1 withV the result that at output junction 88 there is provided a voltage which is a direct and correlated function representative of the voltage accumulated on the timing capacitor C6.

The tube V4 forms a discharge path for the timing capacitor C6 and is of the conventional three-element type having a cathode 90, grid 9|, anode 92 and a cathode heater 93. The cathode is connected to the cathode terminal 81 on the ground line 86, the anode 92 being connected to junction on the charging line 10 connected to the positive terminal of the timing capacitor C6. The conductivity of the discharge tube V4 depends upon the voltage impressed upon it through condenser C1 in line 83. The voltage of the grid of tube V4 is shown in Figure 6. The grid is normally maintained at a voltage level such that the tube is non-conductive and it simply remains non-conductive through the negative terminal of the timing capacitor C6. Tube V4 soon returns to the non-conductive state due to the dissipation of its positive grid-charge through resistor R8 to negative line 83.

The charging of timing capacitor C6 is by means of the -positive output line 43, thence through Junction 18, resistor RIU, junction 1l and resistor R9 to the positive terminal of the timing capacitor C6. The values of resistor R9 and timing capacitorv C6 are regulated so'that the timing capacitor never quite reaches full charge during the longest interval for which the instrument is designed, and consequently the voltage across the timing capacitor serves as a measure of the elapsed time interval from the last received signal.

As previously explained the voltage oi' the timing capacitor C6 (which controls and is reflected by the voltage of the cathode follower tube V3 at output junction 88 of the latter) serves to determine the voltage of a holding capacitor illustrated in Figure l at C8. The holding capacitor C8 is connected from ground terminal 94 to junction 95. The transfer .of the potential of terminal 88 of the cathode follower tube V3 to the holding capacitor C8 is accomplished by means of a pair of transfer tubes V5 and V6. 'I'hese are identical three-element tubes, the tube V5 con- .sist-ing of a cathode 96, grid 91 and anode 98. The transfer tube V6 likewise has a cathode |00, grid |0| and anode |02. Line |03 is connected to the cathode (output) terminal 88 of the first cathode follower tube V3, and extends to the plate terminal I 04 of tube V6 and thence to the cathode 96 of the transfer tube V5. Terminal 95 of the holding capacitor C8 is connected through line |05 to the cathode terminal |06 of transfer tube V6 and thence to the anode 98 of the .transfer tube V5. The grid |0| of the tube V6 is connected to the grid 91 of tube V5 and thence to junction 62. Junction 62 is connected through line 6| and capacitor C5 to the plate terminal of the multivibrator tube V2.

Multivibrato-r tube V2 is normally conductive and it becomes `non-conductive as illustrated by the positive square wave in Figure 4. When the plate of multivibrator tube V2 thus becomes positive, this voltage (of plate terminal 48) is impressed through capacitor C5 upon junction 62 and the grids 91 and |0| of transfer tubes V5 and V6, which hence become positive instantaneously at time X as shown in Figure 5. This positive pulse on the grids 91 and |0| soon dissipates to ground 63 via resistor RI2, the time of' dissipation being illustrated by interval B of Figure 5. The transfer tubes V5 and V6 are hence conductive for a short instant and this is equivalent to the establishment of a connection between junction 88 on the first cathode follower tube V3 and the terminal of the holding capacitor C8. The iiow of current between these junctions depends upon whether the holding capacitor has been charged at a higher voltage than existing at junction 88 or whether the reverse is true. The current ow is through either the tube V5 or the tube V6 since these tubes are inverted with respect to each other and both become conductive at the same instant. When the voltage at junction 88 is higher than that at terminal 95 of the holding capacitor C8, current ows through line |03 to the anode |02 of tube V6 and thence to the cathode |00, through line |05 to the terminal 95. When the voltage at terminal 95 of the holding capacitor C8 is higher than at junction 88 of the rst cathode follower, the current ow is from terminal 95 through line |05 to anode 98 to the cathode 96 of the transfer tube V5 and thence through plate terminal |04 of line |03 to terminal 88 of the first cathode follower tube V3. This action serves in any event to equalize the voltage between the holding canaar? y o pacitor C8 and terminal 88, anni tubes V8 and V8 then return to the non-conductive condition.

Immediately thereafter (time Y, Figures 2-7) the timingcapacitor C8 is discharged as previously described, but when this occurs the grids 81 and |I of the transfer tubes V8 and V8 (Figure 5i `are negative and the transfer tubes arenonconductive. The negative swing during interval C (Figure has no effect. Hence` the voltage transferred to the holding capacitor G8 is maintained for its useful purpose andthe timing capacitor C6 again begins to charge.

'I'he voltage across the holding capacitor C8 may be utilized directly but is preferably utilized for the control of a second cathode follower tube V1 of the same type as tube V3. Tube V1 has an indirectly heated cathode |08, a grid |09 and an anode H0. The cathode is heated indirectly by the nlament H2. The positive junction 88 of the holding capacitor C8 is connected to the grid |09 and thereby controls 'the current passed through the second cathode follower'tube V1 which flows by a circuit extending from ground 84 through resistance RI 3, junction I I to cathode -|08 and thence through the tube V1 to the anode H0 and thence by line H3 through junction H4 to junction 80 on the positive feed line 43'.

The output voltage is the voltage existing between junctions and H4 (or from to ground, if desired) and this is utilized through a network of resistors shown generally opposite the bracket H5. One circuit through the resistor network extends from junction ||4 on line H3, through resistor RI5 and through the upper part of resistor RIG to tap H6, thence to junction H1 and through line ||8 to junction |20, and thence through more or less of resistor R|4 and through the milliammeter M, through line |2|, junction |22 and thence to junction IH. The circuit also extends from variable tap I I8 through the lower part of resistor RIB, through resistor R|1 to ground |24. By adjusting the variable tap H6 on resistor R|6, it is possible to balance the voltage at this point so that it equals the voltage at junction III and thereby allowing adjustment of the meter M to the zero point of the scale. This adjustment is made when the output between points III and ||4- is at the highest frequency rate (pulse rate) that the iustrument is designed to handle. Thus, where the scale of meter M is calibrated to read from 240 pulse beats per minute to 40 beats per minute,

the instrument is calibrated against any suitable standard producing 240 beats per minute, and with the output so established the variable tap H8 is adjusted until the meter M reads zero.

A portion of resistor R|4 is bridged by the variable short circuiting line extending from junction |20 through line |25 to the variable tap |26. This adjustment allows the meter M to be brought to full scale at the minimum frequency -rate for which the system is designed. Thus,

where the instrument is designed] to register a minimum pulse rate of 40 pulse beats per minute, a frequency of this magnitude from a suitable standard is'impressed upon the input terminals and the adjustable tap |26 is varied, shorting out more or less of resistor R|4 until the meter reading is brought to the maximum point on the scale. The meter M is then calibrated at intermediate frequencies so as to establish various points on the meter scale.

Where it is desired to utilize the voltage output for the operation of a galvanometer or for the operation of any suitable work circuit the output is taken off-the resistor v -juxiction H1, throughl resistor Ril, to junction network extending from |21 and thence through more or less of the'variable resistor R|8 to junction |28 and thence through more or less of the variable resistor R28 .and through the resistor R2| to Junction |28.

' (galvanometer) resistances R|8 and.R|8 are included, for by decreasing or increasing the total value of RIB plus R|9, the current through the exterior instrument can be raised or lowered.

A conventional power supply for the instrument is provided from alternating current lines ACI and AC2 which are connected through a snap switch |38 and fuse |39 to the primary winding |40 of a transformer TI having a plurality of secondary windings X', Y', Z', F' and P'. The

winding X' has its midpointgrounded at |42 and its terminals X-X serve to supply filament current to the filaments 35' and 36 of the multivibrator tubes VI and V2, to the filaments 14 and |2 of the rst and second cathode follower tubes V3 and V1 and-to the lamen- 93 of the discharge tube V4. The winding Y having output terminals Y-Y serves to supply current to the cathode heater filament |09'. of the transfer tube V6, while the winding Z' having output terminals Z-Z serves to supplyillament current -to the lament 86 of the transfer tube V5. The

winding F' serves to supply current to the fila-- |45 of the winding P is connected to line |46'ex-l tending through junctions |41 and |48 to the output terminal 82 of the power pack. The cathode |43 is connected through line |41 to junction |48 and through the inductance LI to junction |50 and thence through resistance R23 to the positive output terminal 8| of the power pack. A condenser C9 is connected across junctions |41 and |49 and a condenser CIO across junctions |48 and |50. vA pair of voltage regulator tubes V9 and V|0 of critical voltage gas-discharge type are connected in series and are grounded at junction |52 by means of ground |53 and the circuit is. extended from junction I 52, through resistor R22 to the negative output terminal 82.

Operation It is assumed for purposes of illustration that the pulse rate as determined by the time interval between the prior two successive pulses is 1/240 of a minute and that the timing capacitor C6 has been charged through resistors R9 and RIU to ia value indicative of this time interval. `Since the grid 1| of the first cathode follower tube V3 is connected to the positive terminal of the timing capacitor C6, the current flowing through the tube V3 is therefore a function of the grid voltage and at junction 88 there occurs a voltage with respect to ground that is likewise a function of the timing capacitor voltage. As the next successive pulse occurs, the multivibrator generates the 9 iiegative square wave at the voltage of the plate of tube VI illustrated in Figure 3 and the positive square wave at the plate of tube V2 as indicated by Figure 4. The positive square wave has the eilect of impressing a positive voltage on the grids 81 and i0| of the transfer tubes V5 and V6 as illustrated by Figure 5, portion B, and the transfer tubes accordingly become conductive. This serves in effect to connect the terminal 95 of the holding capacitor C8 to terminal 88 of the ilrst cathode follower tube V3 and the holding capacitor either charges or discharges as the case may be, depending upon whether its voltage is less or more than the voltage at junction Il.

It will be noted that the grids of V5 and V6 are returned to chassis through R12 but that both cathodes are connected to points positive with respect to chassis, V5 cathode to Junction 88 and V6 cathode to junction 95. This results in a negative grid to cathode voltage on V5 equal to the voltage across R1 and a negative grid to cathode voltage on V6 equal to the voltage across C8. Thus, both V5vand V6 are normally nonconductive.

It may be noted that when the voltage across R1 is a minimum due to the discharge of condenser C6, the grids of tubes V5 and V8 are made first cathode follower V3 again is transferred to the holding capacitor C8. In this instance, however, the voltage is greater since a longer time interval for` charging had elapsed and the holding capacitor C8 hence charged to the higher voltage. This has the effect of increasing the current flow through the second cathode follower tube Vl and, hence the voltage at point III immediately becomes more positive, with the result that a potential is impressed upon the meter M. Since it is assumed that the meter has already been calibrated at the beats per minute rate, the meter then would indicate 40 on the scale.

Thus, a diagnostician utilizing the instrument may observe that the needle of the instrument M moves quickly from one scale reading to the other, either up or down, or may remain steady. 'I'he possibility that the meter may move to/another scale reading occurs once for each input signal received; whether or not it does move to a new position depends upon whether the signal impulse rate has changed. The meter M is preferably of the aperiodic type and is preferably suff ficiently sensitive so that it quickly assumes a new reading where this occurs. Where the needle moves up or down, this indicates that further negative by the portion of the differentlated multivibrator pulse, Figure 5, interval C.

As the grids 91 and |0| again assume their normal value, as illustrated in Figure 5, the transfer tubes V5 and V6 become non-conductive, the negative voltage impressed upon these grids at time C, Figure 5, being ineifective inasmuch as the tubes at that time are already non-conductive. The charge thus transfers to the holding capacitor C8, establishing a predetermined voltage across it, and this voltage in turn establishes a definite current flow through the second cathode follower tube VI. Since the instrument is assumed already to have been calibrated, this current flow through the second cathode follower tube establishes a potential on the junction III which is equal to that established at IIS and the meter is not deflected, i. e. it remains at the 240 per minute scale mark (i. e. the zero current posi tion of the meter).

The negative square wave occurring at the plate of multivibrator tube Vi illustrated in Figure 3 has no eiect as it swings to the negative since it serves merely to produce a more negative voltage on the grid 9| of the discharge tube V4. This is illustrated in Figure 6, time interval D. However, as the multivibrator tube completes its vibration and the negative voltage at the plate of tube VI again decreases to a steady state value, time Y, a positive voltage is impressed upon the grid 9| of the discharge tube V4 as illustrated during time interval E, Figure 6, and this normally non-conductive tube becomes conductive and thus serves as a discharge path for the timing capacitor C6 through the circuit previously described. After the short time interval E, Figure 6, the discharge tube V4 again becomes non-conductive and the timing capacitor C6 again begins to charge through resistor R9 and RIU through the circuit previously described. The charge continues through the time interval elapsing until the next pulse is received and, for purposes of illustration, it is assumed that a longer period of time elapses equivalent to say 40 heartbeats per minute.`

When the next heartbeat signal is impressed upon the input terminals 30-3I, the cycle is repeated and the voltage at terminal 88 on the there is a variation in the instantaneous rate of pulse, the amount of variation being indicated by the position of the meter needle on the scale.

By utilizing a cathode ray oscillograph connected to the outputA terminals ISI-|33, there' may be indicated, with reasonable accuracy, impulse rates in much higher frequency than may be indicated by a mechanical instrument such as the meter M. A meter such as that illustrated at M and heretofore described is well adapted for the relatively slow pulse rates encountered,y

in cardiographic diagnosis. By suitable variation in constants the instrument and method of/the presentinvention may be utilized for indicating or operating work circuits in accordance with instantaneous acceleration of mechanical and electrical apparatus, and for other rate functions, at frequency ranges much above or below those here specically illustrated.

As many apparently widely diierent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to ybe understood that we do not limit ourselves to the specific embodiments herein except as dened by the appended claims.

What we claim is:

1. An apparatus for establishing a voltage characteristic, the magnitude of which is a function of the time interval elapsing between successive impulses received, which comprises a storage condenser, a holding condenser, a thermionic voltage follower responsive to the voltages across the storage condenser, means for gradually charging said storage condenser during the time intervals between successive signal impulses received, means for generating a timing impulse in response to the reception of each signal impulse, means responsive to the timing impulse so generated for charging said holding condenser to a voltage whichis a function of the voltage produced on the voltage follower of the storage condenser and for then discharging said storage condenser, and a voltage follower responsive to the voltage so established on the holding condenser. i

2. 'Ihe apparatus of claim 1 further characterized in that the means for generating a timt ing impulse comprises multivibrator thermionic tube networlr.

3. In a cardiotachometer system including means for deriving the heartbeat signal of a patient, the improvements comprising a storage condenser, a holding condenser, means for gradually charging said storage condenser during the time interval between successive heartbeat signals, a thermionic voltage follower network connected to the storage condenser for continuously establishing a voltage which ls a function of the voltage across the storage condenserI means for generating a timing impulse in response to each heartbeat signal received, means responsive to said timing impulse for charging the holding condenser from said thermionic voltage follower and for Ithen discharging said storage condenser, and means responsive to the voltage across the holding condenser for showing the `duration of time between successive heartbeat signals.

4. The apparatus in claim 3 further characterized in that the means responsive to the voltage across the holding condenser is an electrical measuring instrument.

5. 1n a cardiotachometer system having means for deriving the heartbeat signal of a patient, the improvements comprising a storage condenser, a holding condenser, means for gradually charging said storage condenser during the time interval between successive heartbeat signals, a first thermionic voltage follower network connected to the storage condenser for continuously establishing a voltage which is a function of the voltage across the storage condenser, means for generating a timing impulse in response to each heartbeat signal received, means responsive to said timing impulse for charging a holding condenser from said thermionic voltage follower and for then discharging said storage condenser, a second voltage follower network connected to the holding condenser for continuously establishing a voltage which is a function of' the voltage across the holding condenser, and means responsive to the voltage established by the second voltage follower.

6. The apparatus of claim 5 further characterized in that the means responsive to the voltage established across the second voltage follower is an electrical current measuring 'ins strument.

7. The apparatus of claim 5 further char,- acterized in that the means for generating timing impulse comprises a :multivibratorafzieti work capable of generating a single squaretva for each input signal received.

includes a resistor network.

9. The apparatus of claim 5 further char-l acterized in that the means responsive to the voltage established by the second voltage follower.'

includes an electrical measuring instrument and a potentiometer network for adjusting the instrument to zero deflection for a predetermined rate of impulses received and resistor means for adjusting the maximum deflection thereof for a predetermined other rate of impulses received.

10. The method of establishing an operating condition which is a function of the time elapsing between successive signal impulses which comprises from a power source independent of received signals applying an electrical charge at a constant gradual rate to a first condenser for a time period which is a function of the time acteristic, the magnitude of which is a function of the time interval elapsing between successive signal impulses received, which comprises from a power source independent of received signals applying a charge at a constant rate to a condenser during the time interval between successive signal impulses, generating a timing impulse in response to the reception of each signal impulse, said timing impulse being only a fraction as long as the shortest time interval between received signals utilizing the beginning of each timing impulse to transfer the charge accumulated on the condenser to a responsive circuit, establishing a voltage characteristic in said responsive circuit which is a function of the voltage accumulated on said condenser and utilizing the termination of each impulse to discharge the condenser preparatory to the next cycle of operation.

12. The method of establishing a voltage characteristic, the magnitude of which is a function of the time interval elapsing between successive signal impulses received, which comprises from a source separate from said signal and at a constant rate charging a storage condenser during the time interval between successive signal irnpulses received, generating a timing impulse in response to the reception of each signal impulse, said impulse being onlya fraction as long as the shortest time interval between received signals, utilizing the beginning of each such timing impulse to establish a voltage on a holding condenser, said voltage being proportional to the voltage established by the accumulated charge on the storage condenser, utilizing the termination of each timing impulse for discharging the g5 storage condenser, and establishing a voltage characteristic responsive to the charge on the holding condenser.

13. An apparatus for establishing an operating condition which is a function of the time interval elapsing between successive signal impulses comprising a capacitor storage element, means independent of said signals including a power source and. resistance connected to said capacitor for V"lying, an electrical charge to said capacitor storage element at a constant rate such that the 8. The apparatus of claim 5 further char#4 acterized in that the means responsive tothe voltage established by the second voltage follower*v .f instantaneous value of the voltage across said capacitor storage element at any time is a function of the time period elapsed since the previous signalV impulse, and a responsive circuit including Y(i0 aholding capacitor and means for instantaneously connecting it to the capacitor storage element for establishing a voltage on said holding capacitor which is a function of the voltage across said capacitor storage element and for then instantaneously discharging said capacitor storage element as the next successive impulse is received.

14. An apparatus for establishing an electrical operating condition which is a function of the time elapsing between successive signal impulses,

first and second condensers, means independent of said signal source including a power source and resistance connected to the first condenser for applying an electrical charge at a constant rate to a first condenser during the period elapsing between successive impulses, means including 13 a generator of timing impulses having a duration of only a fraction of the time elapsing between the most rapidly received signal impulses and including thermionic tube circuits responsive vto said generator of timing impulses and connecting the rst and second condensers for establishing a. voltage on the second condenser which is proportionalof the charge on the first condenser and immediately thereafter discharging the first condenser as each impulse is received, and means responsive to the charge on the second condenser.

15. The apparatus of claim 14 further characterized in that the means responsive to the voltage of said second condenser is an indicating instrument.

16. An apparatus for establishing a voltage characteristic, the magnitude of which is a function .of the time interval elapsing between successive signal impulses received from a signal source which comprises a condenser, means including a power source independent of said signals and connected through a resistance to said condenser for charging said condenser at a constant rate in the time between successive signal impulses, impulse generator means connected to said signal source for generating a timing impulse in response to each signal impulse received, said timing impulse having a duration which isv only a fraction as long as the shortest time elapsing between received signal impulses, thermionic tube means connected to said impulse generator means and to said condenser and responsive to the beginning of each timing impulse for establishing a voltage in a work -circuit responsive to the voltage accumulated on said condenser and responsive to the termination of each impulse to discharge the condenser preparatory to the next cycle of operation.

17. An apparatus for establishing a voltage characteristic, the magnitude of which is a function of the time interval elapsing between successive impulses received rom a signal source, which comprises a storage condenser, a holding condenser, means including a power source independent of said, signal source and connected through a resistor to said condenser for charging said storage condenser at a constant rate during the time intervals elapsing between successive signal impulses received, impulse generator means connected to said signal source for generating a timingY impulse in response to the reception of each signal impulse,` thermionic voltage supply and circuit control means connected to said impulse generator means and to said storage and holding condensers and responsive to each timing impulse of the impulse generator means for first charging the holding condenser to a Voltage which is a function of the voltage across the storage condenser and for then discharging the storage condenser, and means responsive to the voltage of the holding condenser.

RALPH K. BOLAND.

BOYNTON G. HAGAMAN.

'REFERENCES CTED UNITED STATES PATENTS Number Name Date 2,021,766 Bivens Nov. 19, 1935 2,121,117 Conover June 21, 1938 2,186,727 Martin et a1. Jan. 9, 1940 2,271,478 Eldredge Jan. 27, 1942 2,294,015 Salb et a1. Aug. 25, 1942 2,301,195 Bradford Nov. 10, 1942 2,335,265 Dodington Nov. 30, 1943 2,359,447 Seeley Oct. 3, 1944 2,372,017 Rogers Mar. 10, 1945 2,377,757 Clark June 5, 1945 2,377,969 Richter June 12, 1945 2,403,557 Sanders July 9, 1946 2,411,573 Holst et al. Nov. 26, 1946 2,415,567 Schcenfeld Feb. 11, 1947 

